What is it about tax havens that makes the G20 leaders so keen to crack down on them? Outrage against all those Russian mafia bosses secretly laundering their prostitution and protection racket money through Luxembourg or disgust at Third World dictators being able to siphon millions of their people’s money into numbered Swiss bank accounts in case they need to make a quick exit one day?

Or is it just envy – the feeling of unfairness that billionaires can sip cocktails on their yachts off Bermuda, paying nothing in tax, while poorer mortals like us have to work and slave?

It’s probably a combination of all three, because G20 politicians have hated tax havens for so long that they’ve started to believe their own spin on the subject. But the business of tax havens is actually far more prosaic than any of these rather exotic images. And the real reason why our leaders hate them is that they simply can’t stand the competition.

If you want to pay less tax – as about five billion of the world’s population doubtless do – you have two options. You can evade taxes, concealing your income from the authorities, which is, of course, illegal. Or you can avoid taxes, which is perfectly legal. You might simply claim the full deductions allowed by the tax authorities or maybe move your money into a place where taxes are lower.

It’s avoiders, not evaders, who are the tax havens’ staple customers. The image of drug money being washed through the Cayman Islands is the stuff of thrillers rather than reality. Criminals generally launder money at home because it’s far riskier to move it across borders. The bread and butter of tax havens is people like you or me, who put their modest life savings into a respected investment company in the Isle of Man. And we do it because that way our savings don’t get clobbered for capital gains tax every time our account manager decides to sell one batch of shares and buy another.

Few honest people have qualms against clamping down on criminals. But despite all the Godfather-style spin, it’s actually the rest of us whom the politicians want to clamp down on. They figure – correctly – that if we remain at liberty to put our money in the Virgin Islands or some other place where taxes are lower, we are likely to do just that. And our ability to escape puts limits on just how much they can tax us.

This explains why even Gordon Brown is calling for curbs on tax havens, despite the fact that many of them, including the Channel Islands, are British dependencies. Other countries want even tougher sanctions.

It’s pure financial protectionism. The G20 leaders signed a communiqué praising free trade and deploring anticompetitive barriers in goods and services. That’s because leaders don’t make goods and services. But they do make taxes and are really keen to keep out the competition in that sector. They don’t mind us shopping around the world for the cheapest goods, but they certainly do mind us shopping around for the cheapest taxes.

They have only themselves to blame. It’s not just that governments seem unable to rein in their bureaucracies and keep their costs under control. It’s that they have made taxes so complicated. The last time I looked, the UK tax code ran to 9,973 pages, and that was back in 2007. Complexity inevitably creates loopholes – which lean, nimble tax havens are delighted to help people exploit.

Many countries have lower taxes on foreigners who invest there. That’s because they figure their own residents are largely captive. But they know that international investors can put their money anywhere in the world, so countries have to make themselves attractive in order to pull them in. When you have two different tax rates for the same thing, however, you must expect trouble. And you get it. What happens is that domestic investors simply send their money to a tax haven, then send it back again as if it were “foreign" investment and pocket the difference in the rates.

You can’t blame the tax havens for this kind of wheeze. The root cause is high and complicated taxes. The surest way for the G20 to get rid of tax havens would be to cut and simplify their own taxes – to take on the competition directly.

Until they do, that competition serves a useful purpose for the public. It does make politicians think twice about adding to tax rates or complexity. In particular it limits the burden they can put on savings and investment – the engine of economic growth.

If tax havens boast some of the highest living standards on the planet, that’s got very little to do with money laundering. It’s because low taxes encourage enterprise, stimulate growth and promote personal freedom, too. Rather than trying to kill tax havens, wouldn’t the world be better if our politicians instead sought to beat them at their own game?